Optical modulator and package

ABSTRACT

An optical modulator includes a dielectric layer and a waveguide. The waveguide is disposed on the dielectric layer. The waveguide includes an electrical coupling portion, a slab portion, and an optical coupling portion. The slab portion is sandwiched between the electrical coupling portion and the optical coupling portion. The slab portion has at least two sub-portions having different heights. A maximum height of the slab portion is smaller than a height of the electrical coupling portion.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of and claims thepriority benefit of a prior application Ser. No. 16/514,993, filed onJul. 17, 2019. The entirety of the above-mentioned patent application ishereby incorporated by reference herein and made a part of thisspecification.

BACKGROUND

Electrical signaling and processing have been the mainstream techniquesfor signal transmission and processing. Optical signaling and processinghave been used in increasingly more applications in recent years,particularly due to the use of optical fiber-related applications forsignal transmission. Accordingly, the devices integrating opticalcomponents and electrical components are formed for the conversionbetween optical signals and electrical signals, as well as theprocessing of optical signals and electrical signals.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a schematic diagram illustrating optical communication in anelectronic device 10 in accordance with some embodiments of thedisclosure.

FIG. 2 is a schematic cross-sectional view illustrating the package inFIG. 1.

FIG. 3A to FIG. 3D are schematic cross-sectional view illustrating amanufacturing method of the optical modulator in the package of FIG. 2.

FIG. 4 is a perspective view illustrating the optical modulator in thepackage of FIG. 2.

FIG. 5 is a schematic cross-sectional view illustrating an opticalmodulator in accordance with some alternative embodiments of thedisclosure.

FIG. 6 is a schematic cross-sectional view illustrating an opticalmodulator in accordance with some alternative embodiments of thedisclosure.

FIG. 7 is a schematic cross-sectional view illustrating an opticalmodulator in accordance with some alternative embodiments of thedisclosure.

FIG. 8 is a schematic cross-sectional view illustrating an opticalmodulator in accordance with some alternative embodiments of thedisclosure.

FIG. 9 is a schematic cross-sectional view illustrating an opticalmodulator in accordance with some alternative embodiments of thedisclosure.

FIG. 10 is a schematic cross-sectional view illustrating an opticalmodulator in accordance with some alternative embodiments of thedisclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

FIG. 1 is a schematic diagram illustrating optical communication in anelectronic device 10 in accordance with some embodiments of thedisclosure. Referring to FIG. 1, the electronic device 10 includes apackage P1 and a package P2. In some embodiments, the package P1 and thepackage P2 are optically communicated with each other through an opticalwaveguide (not shown). Details regarding the optical communicationbetween the package P1 and the package P2 are described below.

In some embodiments where the package P1 serves as a transmitter, thepackage P1 may include a SoC (system-on-chip) (Tx) die, a driver, and anoptical signal source OP1. In some embodiments, the SoC (Tx) die isreferred to as a “processor.” In some embodiments, the driver iselectrically connected to the processor (SoC (Tx) die) and is configuredto drive the optical modulator 500 of the optical signal source OP1. Insome embodiments, the optical signal source OP1 may include a lightsource (e.g., a VCSEL diode) and an optical modulator 500. In someembodiments where the package P2 serves as a receiver, the package P2may include a SoC (Rx) die, an amplifier, and a photo-detector OP2.During the optical communication between the package P1 and the packageP2, the SoC (Tx) die generates and transmits an electrical signal to thedriver. Meanwhile, the driver controls the optical modulator 500 in theoptical signal source OP1 based on the electrical signal generated fromthe SoC (Tx) dies of the package P1 such that the light beam emittedfrom the light source and irradiated onto the optical modulator 500 canbe modulated to generate an optical signal. The optical signal generatedby the optical modulator 500 is transmitted to and received by thephoto-detector OP2 of the package P2. Subsequently, the photo-detectorOP2 converts the optical signal into a photo-current (another electricalsignal) and the photo-current is amplified by the amplifier. Theamplified electrical signal is then transmitted to the SoC (Rx) die ofthe package P2. The configuration of the package P1 will be described indetail below.

FIG. 2 is a schematic cross-sectional view illustrating the package P1in FIG. 1. For simplicity, the light source in FIG. 1 is not shown inFIG. 2. Referring to FIG. 2, the package P1 includes a substrate 100. Insome embodiments, the substrate 100 may be a silicon substrate, asilicon germanium substrate, or a substrate formed of othersemiconductor materials. In some embodiments, the substrate 100 may bedoped with p-type dopants (such as boron or BF₂), n-type dopants (suchas phosphorus or arsenic), or a combination thereof. Alternatively, thesubstrate 100 may be an intrinsic semiconductor substrate. In somealternative embodiments, the substrate 100 is a dielectric substrateformed of, for example, silicon oxide. In some embodiments, the packageP1 includes a dielectric layer 200 and an insulating layer 700sequentially stacked on the substrate 100. In some embodiments, amaterial of the dielectric layer 200 includes silicon oxide, siliconnitride, titanium oxide, or the like. In some embodiments, thedielectric layer 200 may include a plurality of air gaps. In someembodiments, the insulating layer 700 is formed of a light-transparentmaterial, such as silicon oxide. Although the dielectric layer 200 andthe insulating layer 700 are respectively shown as a bulky layer in FIG.2, it is understood that the dielectric layer 200 and the insulatinglayer 700 may be respectively constituted by multiple dielectric layers.In some embodiments, the dielectric layer 200 may be referred to as“buried oxide layer.”

As illustrated in FIG. 2, the package P1 further includes integratedcircuit devices 400, optical modulators 500, and optical gratingcouplers 600 embedded in the dielectric layer 200 and the insulatinglayer 700. For simplicity, one integrated circuit device 400, oneoptical modulator 500, and one optical grating coupler 600 are shown inFIG. 2. However, it should be understood that the package P1 may includemore than one integrated circuit devices 400, more than one opticalmodules 500, and more than one optical grating coupler 600. In someembodiments, the integrated circuit devices 400 include active devicessuch as transistors and or/diodes (which may include photo diodes). Insome embodiments, the integrated circuit devices 400 may also includepassive devices such as capacitors, resistors, or the like. In someembodiments, the SoC (Tx) die and the driver in FIG. 1 are formed by theintegrated circuit devices 400.

In some embodiments, a portion of each optical modulator 500 is embeddedin the dielectric layer 200 while another portion of each opticalmodulator 500 is embed in the insulating layer 700. In some embodiments,the optical modulators 500 are used for modulating optical signals. Theconfiguration and the formation method of the optical modulators 500will be discussed in detail later.

In some embodiments, the optical grating couplers 600 are embedded inthe dielectric layer 200 and are covered by the insulating layer 700. Asillustrated in FIG. 2, top portions of the optical grating couplers 600have grating, so that the optical grating couplers 600 have the functionof receiving light or transmitting light. In some embodiments, theoptical grating couplers 600 receive the light from the overlying lightsource or optical signal source (not shown) and transmit the light tothe optical modulator 500 through a waveguide (not shown).

As illustrated in FIG. 2, the package P1 further includes a plurality ofthrough vias 300 embedded in the substrate 100, the dielectric layer200, and the insulating layer 700. In some embodiments, the through vias300 may be referred to as “through semiconductor vias” or “throughsilicon vias.” It is worth to note that although the through vias 300are illustrated as not penetrating through the substrate 100 in FIG. 2,the disclosure is not limited thereto. In some alternative embodiments,the through vias 300 may penetrate through the substrate 100, thedielectric layer 200, and the insulating layer 700. In some embodiments,the through vias 300 are formed of a conductive material. For example,the through vias 300 may include a metallic material, such as tungsten,copper, titanium, aluminum, nickel, alloys thereof, or the like. In someembodiments, an isolation layer 302 is formed to encircle the throughvias 300. For example, the isolation layer 302 may be formed to coversidewalls and a bottom surface of each through via 300. In someembodiments, the isolation layer 302 electrically isolates the throughvias 300 from the substrate 100. For simplicity, two through vias 300are shown in FIG. 2. However, it should be understood that the number ofthe through via 300 in the package P1 may be adjusted based on demand.

In some embodiments, an interconnect structure 800 is formed over theinsulating layer 700. The interconnect structure 800 includes aninter-dielectric layer 810, a plurality of patterned conductive layers820, and a plurality of conductive vias 830. For simplicity, theinter-dielectric layer 810 is illustrated as a bulky layer in FIG. 2,but it should be understood that the inter-dielectric layer 810 may beconstituted by multiple dielectric layers. The patterned conductivelayers 820 and the dielectric layers of the inter-dielectric layer 810are stacked alternately. In some embodiments, the conductive vias 830are embedded in the dielectric layers of the inter-dielectric layer 810.In some embodiments, two adjacent patterned conductive layers 820 areelectrically connected to each other through conductive vias 830. Insome embodiments, the interconnection structure 800 is electricallyconnected to the through vias 300 and the optical modulator 500. Forexample, the bottommost patterned conductive layer 820 is directly incontact with the through vias 300 and the optical modulator 500 torender electrical connection between the interconnect structure 800 andthe through vias 300 and between the interconnect structure 800 and theoptical modulator 500. Although not illustrated, it should be understoodthat the integrated circuit devices 400 may be electrically connected tothe interconnect structure 800 through conductive layers not shown inFIG. 2.

In some embodiments, the inter-dielectric layer 810 may be formed ofsilicon oxide, silicon oxynitride, silicon nitride, or low-k dielectricmaterials having k values lower than about 3.0. The low-k dielectricmaterials may include Black Diamond (a registered trademark of AppliedMaterials), a carbon-containing low-k dielectric material, HydrogenSilsesQuioxane (HSQ), MethylSilsesQuioxane (MSQ), or the like. Etch stoplayers (not shown) may be formed to separate neighboring dielectriclayers within the inter-dielectric layer 810. In some embodiments, theetch stop layers are formed of a material having a high etchingselectivity relative to the dielectric layers of the inter-dielectriclayer 810. For example, the etch stop layers may be formed of siliconcarbide, silicon carbo-nitride, or the like. The inter-dielectric layer810, for example, may be formed by suitable fabrication techniques suchas spin-on coating, chemical vapor deposition (CVD), plasma-enhancedchemical vapor deposition (PECVD), or the like. In some embodiments, amaterial of the patterned conductive layers 820 and a material of theconductive vias 830 include aluminum, titanium, copper, nickel,tungsten, and/or alloys thereof. The patterned conductive layers 820 andthe conductive vias 830 may be formed by, for example, electroplating,deposition, and/or photolithography and etching. In some embodiments,the patterned conductive layers 820 and the underlying conductive vias830 are simultaneously formed. It should be noted that the number of thedielectric layers in the inter-dielectric layer 810, the number of thepatterned conductive layers 820, and the number of the conductive vias830 shown in FIG. 2 are merely exemplary illustrations, and thedisclosure is not limited. In some alternative embodiments, the numberof the dielectric layers in the inter-dielectric layer 810, the numberof the patterned conductive layers 820, and the number of the conductivevias 830 may be adjusted depending on the routing requirements.

As illustrated in FIG. 2, a dielectric layer 900, a plurality ofconductive pads 1000, and a passivation layer 1100 are sequentiallyformed over the interconnect structure 800. In some embodiments, thedielectric layer 900 is formed on the interconnect structure 800 topartially cover the topmost patterned conductive layer 820. For example,the dielectric layer 900 may include a plurality of openings exposingleast a portion of the topmost patterned conductive layer 820. In someembodiments, a material of the dielectric layer 900 may be similar tothat of the inter-dielectric layer 810. For example, the dielectriclayer 900 may be formed of silicon oxide, silicon oxynitride, siliconnitride, or low-k dielectric materials having k values lower than about3.0.

In some embodiments, the conductive pads 1000 are formed over thedielectric layer 900 and the interconnect structure 800. In someembodiments, the conductive pads 1000 extend into the openings of thedielectric layer 900 to be directly in contact with the topmostpatterned conductive layer 820. In other words, the conductive pads 1000are electrically connected to the interconnect structure 800. In someembodiments, a material of the conductive pads 1000 may be similar tothat of the patterned conductive layers 820. For example, the conductivepads 1000 may include aluminum, titanium, copper, nickel, tungsten,and/or alloys thereof. In some embodiments, the conductive pads 1000 areelectrically connected to the through vias 300, the integrated circuitdevices 400, and/or the optical modulators 500 through the patternedconductive layers 820 in the interconnect structure 800.

In some embodiments, the passivation layer 1100 is formed to cover thedielectric layer 900 and the conductive pads 1000. In some embodiments,the passivation layer 1100 has a plurality of openings partiallyexposing each conductive pad 1000 for future electrical connection. Insome embodiments, the passivation layer 1100 includes, for example,polyimide, epoxy resin, acrylic resin, phenol resin, benzocyclobutene(BCB), polybenzoxazole (PBO), or other suitable polymer-based dielectricmaterials. In some embodiments, the passivation layer 1100 may be formedby suitable fabrication techniques such as spin-on coating, CVD, PECVD,or the like.

As illustrated in FIG. 2, openings OP are formed in the package P1. Forsimplicity, one opening OP is shown in FIG. 2. However, it should beunderstood that the package P1 may include more than one openings OP. Insome embodiments, the openings OP penetrate through the passivationlayer 1100, the dielectric layer 900, and the inter-dielectric layer810. In some embodiments, the openings OP further extend into a portionof the insulating layer 700. In some embodiments, the openings OP may beformed by removing a portion of the passive layer 1100, a portion of thedielectric layer 900, a portion of the inter-dielectric layer 810, and aportion of the insulating layer 700 through a photolithography processand an etching process. In some embodiments, locations of the openingsOP correspond to locations of the optical grating couplers 600. Forexample, the openings OP overlap the underlying optical grating couplers600. As such, the number of the openings OP may correspond to the numberof the optical grating couplers 600. In some embodiments, top views ofthe openings OP may take shapes of polygons, circles, or the like. Insome embodiments, when the inter-dielectric layer 810 and the dielectriclayer 900 include low-k dielectric materials, the openings OP may bepassivated by covering sidewalls of openings OP with a conformalnon-low-k dielectric layer (not shown) so that the low-k dielectricmaterials are not exposed. In some embodiments, the light emitted fromthe light source (not shown) may transmit through the openings OP andthe dielectric layer 700 located directly above the optical gratingcouplers 600 to arrive at the optical grating couplers 600.

It is appreciated that the package P1 may include various other devicesand circuits not shown in FIG. 2. These devices and circuits may be usedfor processing and transmitting optical signals and electrical signals.

In some embodiments, the configuration of the optical modulator 500contributes to the performance of the electronic device 10 greatly. Thedetails regarding the optical modulator 500 will be discussed below.

FIG. 3A to FIG. 3D are schematic cross-sectional view illustrating amanufacturing method of the optical modulator 500 in the package P1 ofFIG. 2. Referring to FIG. 3A, the substrate 100 is provided. Asmentioned above, the substrate 100 may be a silicon substrate, a silicongermanium substrate, or a substrate formed of other semiconductormaterials. In some embodiments, the substrate 100 may be doped withp-type dopants (such as boron or BF₂), n-type dopants (such asphosphorus or arsenic), or a combination thereof. Alternatively, thesubstrate 100 may be an intrinsic semiconductor substrate. In somealternative embodiments, the substrate 100 is a dielectric substrateformed of, for example, silicon oxide.

In some embodiments, the dielectric layer 200 is formed on the substrate100. As mentioned above, the dielectric layer 200 includes siliconoxide, silicon nitride, titanium oxide, or the like. In some alternativeembodiments, when the dielectric layer 200 shown in FIG. 2 includes airgaps, the air gaps may be located within the optical modulator 500. Thatis, the portion of the dielectric layer 200 shown in FIG. 3A maycorrespond to the air gap, and the material of the dielectric layer 200shown in FIG. 3A may be air.

As illustrated in FIG. 3A, a semiconductor material SM is formed on thedielectric layer 200. In some embodiments, a material of thesemiconductor material SM and the material of the substrate 100 may bethe same or may be different from each other. For example, thesemiconductor material SM may be made of a suitable elementalsemiconductor, such as crystalline silicon, diamond, or germanium; asuitable compound semiconductor, such as gallium arsenide, siliconcarbide, indium arsenide, or indium phosphide; or a suitable alloysemiconductor, such as silicon germanium carbide, gallium arsenicphosphide, or gallium indium phosphide. In some embodiments, thestructure shown in FIG. 3A may be collectively referred to as a“silicon-on-insulator (SOI) substrate.”

Referring to FIG. 3B, the semiconductor material SM is doped to formvarious regions. For example, the semiconductor material SM may be dopedto form a first region R1, a second region R2, and an optical couplingregion OR sandwiched between the first region R1 and the second regionR2. The first region R1 may be further divided into a first electricalcoupling region ECR1 and a first slab region SR1 arranged side by side.Similarly, the second region R2 may be further divided into a secondelectrical coupling region ECR2 and a second slab region SR2 arrangedside by side. On the other hand, the optical coupling region OR may bedivided into a first optical coupling region OCR1 and a second opticalcoupling region OCR2 arranged side by side. As illustrated in FIG. 3B,the first slab region SR1 is sandwiched between the first electricalcoupling region ECR1 and the first optical coupling region OCR1. On theother hand, the second slab region SR2 is sandwiched between the secondelectrical coupling region ECR2 and the second optical coupling regionOCR2.

In some embodiments, the semiconductor material SM located in the firstelectrical coupling region ECR1, the first slab region SR1, and thefirst optical coupling region OCR1 may be doped with dopants of firstconductivity type. Meanwhile, the semiconductor material SM located inthe second electrical coupling region ECR2, the second slab region SR2,and the second optical coupling region OCR2 may be doped with dopants ofsecond conductivity type. In some embodiments, the first conductivitytype is opposite to the second conductivity type. For example, thedopants of first conductivity type may be p-type dopants and the dopantsof the second conductivity type may be n-type dopants. That is, in someembodiments, the semiconductor material SM located in the firstelectrical coupling region ECR1, the first slab region SR1, and thefirst optical coupling region OCR1 is doped with p-type dopants whilethe semiconductor material SM located in the second electrical couplingregion ECR2, the second slab region SR2, and the second optical couplingregion OCR2 is doped with n-type dopants. In some embodiments, thep-type dopants includes, for example, boron, BF₂, or the like. On theother hand, the n-type dopants includes, for example, phosphorus,arsenic, or the like.

In some embodiments, the doping concentration in each region of thesemiconductor material SM varies. In some embodiments, a dopingconcentration in the first electrical coupling region ECR1 is greaterthan a doping concentration in the first slab region SR1 and the dopingconcentration in the first slab region SR1 is greater than a dopingconcentration in the first optical coupling region OCR1. Similarly, adoping concentration in the second electrical coupling region ECR2 isgreater than a doping concentration in the second slab region SR2 andthe doping concentration in the second slab region SR2 is greater than adoping concentration in the second optical coupling region OCR2. Forexample, the doping concentration in the first electrical couplingregion ECR1 ranges between 1×10²⁰ cm⁻³ and 1×10²² cm⁻³, the dopingconcentration in the first slab region SR1 ranges between 1×10¹⁸ cm⁻³and 1×10²⁰ cm⁻³, and the doping concentration in the first opticalcoupling region OCR1 ranges between 1×10¹⁷ cm⁻³ and 1×10¹⁸ cm⁻³.Similarly, the doping concentration in the second electrical couplingregion ECR2 ranges between 1×10²⁰ cm⁻³ and 1×10²² cm⁻³, the dopingconcentration in the second slab region SR2 ranges between 1×10¹⁸ cm⁻³and 1×10²⁰ cm⁻³, and the doping concentration in the second opticalcoupling region OCR2 ranges between 1×10¹⁷ cm⁻³ and 1×10¹⁸ cm⁻³.

In some embodiments, the semiconductor material SM may be doped by thefollowing step. First, a first photoresist layer (not shown) is formedto cover the first slab region SR1, the first optical coupling regionOCR1, the second optical coupling region OCR2, the second slab regionSR2, and the second electrical coupling region ECR2. Meanwhile, thefirst photoresist layer exposes the first electrical coupling regionECR1 of the semiconductor material SM. Subsequently, an ion implantationprocess is performed on the revealed portion of the semiconductormaterial SM (the first electrical coupling region ECR1) to dope thesemiconductor material SM with dopants of first concentration.Thereafter, the first photoresist layer is removed. Then, a secondphotoresist layer (not shown) is formed to cover the doped firstelectrical coupling region ECR1, the first optical coupling region OCR1,the second optical coupling region OCR2, the second slab region SR2, andthe second electrical coupling region ECR2. Meanwhile, the secondphotoresist layer exposes the first slab region SR1 of the semiconductormaterial SM. Subsequently, another ion implantation process is performedon the revealed portion of the semiconductor material SM (the first slabregion SR1) to dope the semiconductor material SM with dopants of secondconcentration. The second concentration is different from the firstconcentration. Thereafter, the second photoresist layer is removed. Theforegoing steps may be repeated several times to obtain thesemiconductor material SM having different doping concentrations/dopanttypes in the first electrical coupling region ECR1, the first slabregion SR1, the first optical coupling region OCR1, the second opticalcoupling region OCR2, the second slab region SR2, and the secondelectrical coupling region ECR2.

Referring to FIG. 3B and FIG. 3C, portions of the semiconductor materialSM located in the first slab region SR1 and the second slab region SR2are removed to obtain a waveguide WG disposed on the dielectric layer200. In some embodiments, the waveguide WG has the first region R1, thesecond region R2, and the optical coupling region OR between the firstregion R1 and the second region R2. In some embodiments, the waveguideWG is divided into a first electrical coupling portion 510, a first slabportion 520, a first optical coupling portion 530, a second electricalcoupling portion 540, a second slab portion 550, and a second opticalcoupling portion 560. In some embodiments, the first electrical couplingportion 510 is located in the first electrical coupling region ECR1, thefirst slab portion 520 is located in the first slab region SR1, thefirst optical coupling portion 530 is located in the first opticalcoupling region OCR1, the second electrical coupling region 540 islocated in the second electrical coupling region ECR2, the second slabportion 550 is located in the second slab region SR2, and the secondoptical coupling portion 560 is located in the second optical couplingregion OCR2. In some embodiments, the first electrical coupling portion510 is connected to the first slab portion 520, the first slab portion520 is connected to the first optical coupling portion 530, the firstoptical coupling portion 530 is connected to the second optical couplingportion 560, the second optical coupling portion 560 is connected to thesecond slab portion 550, and the second slab portion 550 is connected tothe second electrical coupling portion 540.

In some embodiments, a height H₅₁₀ of the first electrical couplingportion 510, a height H₅₃₀ of the first optical coupling portion 530, aheight H₅₄₀ of the second electrical coupling portion 540, and a heightH₅₆₀ of the second optical coupling portion 560 may be substantially thesame. On the other hand, a maximum height of the first slab portion 520and a maximum height of the second slab portion 550 are smaller than theheight H₅₁₀ of the first electrical coupling portion 510, the heightH₅₃₀ of the first optical coupling portion 530, the height H₅₄₀ of thesecond electrical coupling portion 540, and the height H₅₆₀ of thesecond optical coupling portion 560. In some embodiments, the first slabportion 520 and the second slab portion 550 may respectively include atleast two sub-portions having different heights. In other words, aninterfacial area A1 between the first electrical coupling portion 510and the first slab portion 520 is larger than an interfacial area A2between the first slab portion 520 and the first optical couplingportion 530. Similarly, an interfacial area A3 between the secondelectrical coupling portion 540 and the second slab portion 550 islarger than an interfacial area A4 between the second slab portion 550and the second optical coupling portion 560.

As illustrated in FIG. 3C, the first slab portion 520 is divided into afirst sub-portion 522, a second sub-portion 524, and a third sub-portion526. The first sub-portion 522 is connected to the first electricalcoupling portion 510, the second sub-portion 524 is connected to thefirst sub-portion 522, and the third sub-portion 526 is connected to thesecond sub-portion 524 and the first optical coupling portion 530. Onthe other hand, the second slab portion 550 is divided into a fourthsub-portion 552, a fifth sub-portion 554, and a sixth sub-portion 556.The fourth sub-portion 552 is connected to the second electricalcoupling portion 540, the fifth sub-portion 554 is connected to thefourth sub-portion 552, and the sixth sub-portion 556 is connected tothe fifth sub-portion 554 and the second optical coupling portion 560.

In some embodiments, the first slab portion 520 is ladder shaped. Forexample, the first slab portion 520 takes the form of a staircase andhas multiple steps, and each step corresponds to one sub-portion. Insome embodiments, the height H₅₁₀ of the first electrical couplingportion 510 is greater than a height H₅₂₂ of the first sub-portion 522,the height H₅₂₂ of the first sub-portion 522 is greater than a heightH₅₂₄ of the second sub-portion 524, and the height H₅₂₄ of the secondsub-portion 524 is greater than a height H₅₂₆ of the third sub-portion526. That is, the interfacial area A1 between the first sub-portion 522and the first electrical coupling portion 510 is greater than theinterfacial area A2 between the third sub-portion 526 and the firstoptical coupling portion 530. Similarly, the second slab portion 550 isalso ladder shaped. For example, the second slab portion 550 takes theform of a staircase and has multiple steps, and each step corresponds toone sub-portion. In some embodiments, the height H₅₄₀ of the secondelectrical coupling portion 540 is greater than a height H₅₅₂ of thefourth sub-portion 552, the height H₅₅₂ of the fourth sub-portion 552 isgreater than a height H₅₅₄ of the fifth sub-portion 554, and the heightH₅₅₄ of the fifth sub-portion 554 is greater than a height H₅₅₆ of thesixth sub-portion 556. That is, the interfacial area A3 between thefourth sub-portion 552 and the second electrical coupling portion 540 isgreater than the interfacial area A4 between the sixth sub-portion 556and the second optical coupling portion 560. It should be noted that thenumber of the sub-portions in the first slab portion 520 and the secondslab portion 550 shown in FIG. 3C is merely an exemplary illustration,and the disclosure is not limited thereto. In some alternativeembodiments, the first slab portion 520 and the second slab portion 550may respectively include other number of sub-portions based on need.

In some embodiments, the ladder shaped first slab portion 520 and theladder shaped second slab portion 550 may be formed by a patterningprocess. In some embodiments, the patterning process involves aphotolithography process and an etching process. For example, a thirdphotoresist layer is formed on the doped semiconductor material SM(shown in FIG. 3B) to cover the semiconductor material SM located in thefirst electrical coupling region ECR1, the semiconductor material SMlocated in the first optical coupling region OCR1, the semiconductormaterial SM located in the second optical coupling region OCR2, thesemiconductor material SM located in the second slab region SR2, and thesemiconductor material SM located in the second electrical couplingregion ECR2. The third photoresist layer also covers a portion of thesemiconductor material SM located in the first slab region SR1 whileexposing another portion of the semiconductor material SM located in thefirst slab region SR1. Subsequently, an etching process is performed onthe exposed portion of the semiconductor material SM to form the firstsub-portion 522 in the first slab region SR1. Thereafter, the thirdphotoresist layer is removed. Then, a fourth photoresist layer is formedon the doped semiconductor material SM (shown in FIG. 3B) to cover thesemiconductor material SM located in the first electrical couplingregion ECR1, the semiconductor material SM located in the first opticalcoupling region OCR1, the semiconductor material SM located in thesecond optical coupling region OCR2, the semiconductor material SMlocated in the second slab region SR2, and the semiconductor material SMlocated in the second electrical coupling region ECR2. The fourthphotoresist layer also covers the first sub-portion 522 and a portion ofthe remaining semiconductor material SM located in the first slab regionSR1. Meanwhile, the fourth photoresist layer exposes another portion ofthe remaining semiconductor material SM located in the first slab regionSR1. Subsequently, an etching process is performed on the exposedportion of the semiconductor material SM to form the second sub-portion524 in the first slab region SR1. It should be noted that the etchantrecipe or etching duration may be adjusted to render the secondsub-portion 524 shorter than the first sub-portion 522. Thereafter, thefourth photoresist layer is removed. The foregoing steps may be repeatedseveral times to obtain the ladder shaped first slab portion 520 and theladder shaped second slab portion 550.

Although FIG. 3B and FIG. 3C illustrated that the doping processprecedes the patterning process, it should be understood that thedisclosure is not limited thereto. In some alternative embodiments, thepatterning process shown in FIG. 3C may take place before the dopingprocess shown in FIG. 3B.

As mentioned above, the doping concentrations in various regions of thesemiconductor material SM are different. As such, a doping concentrationof the first electrical coupling portion 510 is greater than a dopingconcentration of the first slab portion 520 and the doping concentrationof the first slab portion 520 is greater than a doping concentration ofthe first optical coupling portion 530. Similarly, a dopingconcentration of the second electrical coupling portion 540 is greaterthan a doping concentration of the second slab portion 550 and the doingconcentration of the second slab portion 550 is greater than a dopingconcentration of the second optical coupling portion 560. For example,the doping concentration of the first electrical coupling portion 510ranges between 1×10²⁰ cm⁻³ and 1×10²² cm⁻³, the doping concentration ofthe first slab portion 520 ranges between 1×10¹⁸ cm⁻³ and 1×10²⁰ cm⁻³,and the doping concentration of the first optical coupling portion 530ranges between 1×10¹⁷ cm⁻³ and 1×10¹⁸ cm⁻³. Similarly, the dopingconcentration of the second electrical coupling portion 540 rangesbetween 1×10²⁰ cm⁻³ and 1×10²² cm⁻³, the doping concentration of thesecond slab portion 550 ranges between 1×10¹⁸ cm⁻³ and 1×10²⁰ cm⁻³, andthe doping concentration of the second optical coupling portion 560ranges between 1×10¹⁷ cm⁻³ and 1×10¹⁸ cm⁻³. In other words, a dopingconcentration gradient may be seen in the waveguide WG. In someembodiments, the first sub-portion 522, the second sub-portion 524, andthe third sub-portion 526 have the same doping concentration. Similarly,the fourth sub-portion 552, the fifth sub-portion 554, and the sixthsub-portion 556 have the same doping concentration.

Referring to FIG. 3D, a plurality of conductive connectors C and theinsulating layer 700 are sequentially formed on the waveguide WG to formthe optical modulator 500. In some embodiments, the conductiveconnectors C are formed on the first electrical coupling portion 510 andthe second electrical coupling portion 540. In some embodiments, amaterial of the conductive connectors C include aluminum, titanium,copper, nickel, tungsten, and/or alloys thereof. In some embodiments,the conductive connectors C are electrically connected to theinterconnect structure 800 (shown in FIG. 2). For example, theconductive connectors C are directly in contact with the bottommostpatterned conductive layer 820 to render electrical connection betweenthe optical modulator 500 and the interconnect structure 800. That is,the conductive connectors C electrically connects the waveguide WG andthe interconnect structure 800. As mentioned above, the insulating layer700 is formed of a light-transparent material, such as silicon oxide.The insulating layer 700 covers the conductive connectors C and thewaveguide WG. For example, the insulating layer 700 laterally covers theconductive connectors C and exposes top surfaces of the conductiveconnectors C for electrical connection. At this stage, the manufacturingprocess of the optical modulator 500 is substantially completed, and theconfiguration of the optical modulator 500 is shown in FIG. 4.

FIG. 4 is a perspective view illustrating the optical modulator 500 inthe package P1 of FIG. 2. For simplicity, the insulating layer 700 ofthe optical modulator 500 is not shown in FIG. 4. Referring to FIG. 4,the optical modulator 500 has the substrate 100, the dielectric layer200, the waveguide WG, the conductive connectors C, and the insulatinglayer 700 (not shown). The dielectric layer 200 and the waveguide WG aresequentially disposed on the substrate 100. In some embodiments, thewaveguide WG is divided into the first electrical coupling portion 510,the first slab portion 520, the first optical coupling portion 530, thesecond electrical coupling portion 540, the second slab portion 550, andthe second optical coupling portion 560. In some embodiments, the firstelectrical coupling portion 510, the first optical coupling portion 530,the second electrical coupling portion 540, and the second opticalcoupling portion 560 are strips parallel to each other. On the otherhand, the first slab portion 520 and the second slab portion 550 arestaircases respectively sandwiched between the first electrical couplingportion 510 and the first optical coupling portion 530 and between thesecond electrical coupling portion 540 and the second optical couplingportion 560. In some embodiments, the strips and the staircases providesufficient length to prevent optical loss during optical transmission.

In some embodiments, the doping concentration of the first electricalcoupling portion 510 is greater than the doping concentration of thefirst slab portion 520 and the doping concentration of the first slabportion 520 is greater than the doping concentration of the firstoptical coupling portion 530. Similarly, the doping concentration of thesecond electrical coupling portion 540 is greater than the dopingconcentration of the second slab portion 550 and the dopingconcentration of the second slab portion 550 is greater than the dopingconcentration of the second optical coupling portion 560. In otherwords, in some embodiments, the first electrical coupling portion 510and the second electrical coupling portion 540 may be referred to as the“heavily doped portion” while the first optical coupling portion 530 andthe second optical coupling portion 560 may be referred to as the“lightly doped portion.” In some embodiments, since the optical signalis transmitted close to/in the first optical coupling portion 530 andthe second optical coupling portion 560, the lightly doped portions (thefirst optical coupling portion 530 and the second optical couplingportion 560) are able to maintain sufficient optical signaltransmission. In other words, the optical loss is minimized. On theother hand, since the electrical signal is transmitted to the firstelectrical coupling portion 510 and the second electrical couplingportion 540, the heavily doped portions (the first electrical couplingportion 510 and the second electrical coupling portion 540) are able toincrease depletion region variation under different voltage bias,thereby providing larger effective refractive index change (A Neff).Moreover, the ladder shaped first slab portion 520 and the ladder shapedsecond slab portion 550 provide sufficient thickness to reduce sheetresistance, thereby minimizing the RC delay. As such, a desiredbandwidth may be effectively obtained. For example, as compared to thestraight slab portions, the ladder shaped first slab portion 520 and theladder shaped second slab portion 550 are able to reduce thetransmission loss by up to 14%, to reduce the slab resistance byapproximately 35%, and to improve the bandwidth by approximately 49%.

FIG. 5 is a schematic cross-sectional view illustrating an opticalmodulator 500 a in accordance with some alternative embodiments of thedisclosure. Referring to FIG. 5, the optical modulator 500 a in FIG. 5is similar to the optical modulator 500 in FIG. 3D, so similar elementsare denoted by the same reference numeral and the detailed descriptionsthereof are omitted herein. The difference between the optical modulator500 a in FIG. 5 and the optical modulator 500 in FIG. 3D lies in thatthe first slab portion 520 and the second slab portion 550 in theoptical modulator 500 a respectively has a doping concentrationgradient. For example, a doping concentration of the first electricalcoupling portion 510 is greater than a doping concentration of the firstsub-portion 522, the doping concentration of the first sub-portion 522is greater than a doping concentration of the second sub-portion 524,the doping concentration of the second sub-portion 524 is greater than adoping concentration of the third sub-portion 526, and the dopingconcentration of the third sub-portion 526 is greater than a dopingconcentration of the first optical coupling portion 530. Similarly, adoping concentration of the second electrical coupling portion 540 isgreater than a doping concentration of the fourth sub-portion 552, thedoping concentration of the fourth sub-portion 552 is greater than adoping concentration of the fifth sub-portion 554, the dopingconcentration of the fifth sub-portion 554 is greater than a dopingconcentration of the sixth sub-portion 556, and the doping concentrationof the sixth sub-portion 556 is greater than a doping concentration ofthe second optical coupling portion 560.

In some embodiments, the doping concentration of the first electricalcoupling portion 510 ranges between 1×10²⁰ cm⁻³ and 1×10²² cm⁻³ and thedoping concentration of the first optical coupling portion 530 rangesbetween 1×10¹⁷ cm⁻³ and 1×10¹⁸ cm⁻³. On the other hand, the dopingconcentration of the first sub-portion 522, the doping concentration ofthe second sub-portion 524, and the doping concentration of the thirdsub-portion 526 respectively range between 1×10¹⁸ cm⁻³ and 1×10²⁰ cm⁻³with a proviso that the doping concentration of the first sub-portion522 is greater than the doping concentration of the second sub-portion524 and the doping concentration of the second sub-portion 524 isgreater than the doping concentration of the third sub-portion 526.Similarly, the doping concentration of the second electrical couplingportion 540 ranges between 1×10²⁰ cm⁻³ and 1×10²² cm⁻³ and the dopingconcentration of the second optical coupling portion 560 ranges between1×10¹⁷ cm⁻³ and 1×10¹⁸ cm⁻³. On the other hand, the doping concentrationof the fourth sub-portion 552, the doping concentration of the fifthsub-portion 554, and the doping concentration of the sixth sub-portion556 respectively range between 1×10¹⁸ cm⁻³ and 1×10²⁰ cm⁻³ with aproviso that the doping concentration of the fourth sub-portion 552 isgreater than the doping concentration of the fifth sub-portion 554 andthe doping concentration of the fifth sub-portion 554 is greater thanthe doping concentration of the sixth sub-portion 556.

In some embodiments, since the optical signal is transmitted close to/inthe first optical coupling portion 530 and the second optical couplingportion 560, the lightly doped portions (the first optical couplingportion 530 and the second optical coupling portion 560) are able tomaintain sufficient optical signal transmission. In other words, theoptical loss is minimized. On the other hand, since the electricalsignal is transmitted to the first electrical coupling portion 510 andthe second electrical coupling portion 540, the heavily doped portions(the first electrical coupling portion 510 and the second electricalcoupling portion 540) are able to increase depletion region variationunder different voltage bias, thereby providing larger effectiverefractive index change (A Neff). Moreover, the ladder shaped first slabportion 520 and the ladder shaped second slab portion 550 providesufficient thickness to reduce sheet resistance, thereby minimizing theRC delay. As such, a desired bandwidth may be effectively obtained. Forexample, as compared to the straight slab portions, the ladder shapedfirst slab portion 520 and the ladder shaped second slab portion 550 areable to reduce the transmission loss by up to 14%, to reduce the slabresistance by approximately 35%, and to improve the bandwidth byapproximately 49%.

FIG. 6 is a schematic cross-sectional view illustrating an opticalmodulator 500 b in accordance with some alternative embodiments of thedisclosure. Referring to FIG. 6, the optical modulator 500 b in FIG. 6is similar to the optical modulator 500 in FIG. 3D, so similar elementsare denoted by the same reference numeral and the detailed descriptionsthereof are omitted herein. The difference between the optical modulator500 b in FIG. 6 and the optical modulator 500 in FIG. 3D lies in thatthe optical modulator 500 b in FIG. 6 is substrate-less. In other words,the substrate 100 shown in FIG. 3D is omitted.

In some embodiments, since the optical signal is transmitted close to/inthe first optical coupling portion 530 and the second optical couplingportion 560, the lightly doped portions (the first optical couplingportion 530 and the second optical coupling portion 560) are able tomaintain sufficient optical signal transmission. In other words, theoptical loss is minimized. On the other hand, since the electricalsignal is transmitted to the first electrical coupling portion 510 andthe second electrical coupling portion 540, the heavily doped portions(the first electrical coupling portion 510 and the second electricalcoupling portion 540) are able to increase depletion region variationunder different voltage bias, thereby providing larger effectiverefractive index change (A Neff). Moreover, the ladder shaped first slabportion 520 and the ladder shaped second slab portion 550 providesufficient thickness to reduce sheet resistance, thereby minimizing theRC delay. As such, a desired bandwidth may be effectively obtained. Forexample, as compared to the straight slab portions, the ladder shapedfirst slab portion 520 and the ladder shaped second slab portion 550 areable to reduce the transmission loss by up to 14%, to reduce the slabresistance by approximately 35%, and to improve the bandwidth byapproximately 49%. Furthermore, since the optical modulator 500 b issubstrate-less, the cost for the substrate may be saved and thecompactness of the device may be enhanced.

FIG. 7 is a schematic cross-sectional view illustrating an opticalmodulator 500 c in accordance with some alternative embodiments of thedisclosure. Referring to FIG. 7, the optical modulator 500 c in FIG. 7is similar to the optical modulator 500 in FIG. 3D, so similar elementsare denoted by the same reference numeral and the detailed descriptionsthereof are omitted herein. The difference between the optical modulator500 c in FIG. 7 and the optical modulator 500 in FIG. 3D lies in thatthe waveguide WG further includes an intrinsic semiconductor portion570. In some embodiments, the optical coupling region OR furtherincludes an intrinsic region IR sandwiched between the first opticalcoupling region OCR1 and the second optical coupling region OCR2. Asillustrated in FIG. 7, the intrinsic semiconductor portion 570 islocated in the intrinsic region IR. In other words, the intrinsicsemiconductor portion 570 is sandwiched between the first opticalcoupling portion 530 and the second optical coupling portion 560. Insome embodiments, the intrinsic semiconductor portion 570 is un-doped.In some embodiments, the first optical coupling portion 530 is dopedwith p-type dopants and the second optical coupling portion 560 is dopedwith n-type dopants. As such, a PIN junction/structure may be formed inthe optical coupling region OR.

In some embodiments, since the optical signal is transmitted close to/inthe first optical coupling portion 530 and the second optical couplingportion 560, the lightly doped portions (the first optical couplingportion 530 and the second optical coupling portion 560) are able tomaintain sufficient optical signal transmission. In other words, theoptical loss is minimized. On the other hand, since the electricalsignal is transmitted to the first electrical coupling portion 510 andthe second electrical coupling portion 540, the heavily doped portions(the first electrical coupling portion 510 and the second electricalcoupling portion 540) are able to increase depletion region variationunder different voltage bias, thereby providing larger effectiverefractive index change (A Neff). Moreover, the ladder shaped first slabportion 520 and the ladder shaped second slab portion 550 providesufficient thickness to reduce sheet resistance, thereby minimizing theRC delay. As such, a desired bandwidth may be effectively obtained. Forexample, as compared to the straight slab portions, the ladder shapedfirst slab portion 520 and the ladder shaped second slab portion 550 areable to reduce the transmission loss by up to 14%, to reduce the slabresistance by approximately 35%, and to improve the bandwidth byapproximately 49%. Furthermore, since a PIN junction/structure is formedin the optical coupling region OR, the power consumption in the opticalmodulator 500 c may be lowered and the optical modulator 500 c may beutilized in ultra-low power applications.

FIG. 8 is a schematic cross-sectional view illustrating an opticalmodulator 500 d in accordance with some alternative embodiments of thedisclosure. Referring to FIG. 8, the optical modulator 500 d in FIG. 8is similar to the optical modulator 500 c in FIG. 7, so similar elementsare denoted by the same reference numeral and the detailed descriptionsthereof are omitted herein. The difference between the optical modulator500 d in FIG. 8 and the optical modulator 500 c in FIG. 7 lies in thatthe waveguide WG has a recess in the optical coupling portion OR. Asillustrated in FIG. 8, an intrinsic semiconductor portion 570 a islocated in the intrinsic region IR. In other words, the intrinsicsemiconductor portion 570 a is sandwiched between the first opticalcoupling portion 530 and the second optical coupling portion 560. Insome embodiments, a height H_(570a) of the intrinsic semiconductorportion 570 a is smaller than the height H₅₃₀ of the first opticalcoupling portion 530. Similarly, the height H_(570a) of the intrinsicsemiconductor portion 570 a is also smaller than the height H₅₆₀ of thesecond optical coupling portion 560. In other words, the intrinsicsemiconductor portion 570 a is the recessing portion of the waveguideWG. In some embodiments, the intrinsic semiconductor portion 570 a isun-doped. In some embodiments, the first optical coupling portion 530 isdoped with p-type dopants and the second optical coupling portion 560 isdoped with n-type dopants. As such, a PIN junction/structure may beformed in the optical coupling region OR.

In some embodiments, since the optical signal is transmitted close to/inthe first optical coupling portion 530 and the second optical couplingportion 560, the lightly doped portions (the first optical couplingportion 530 and the second optical coupling portion 560) are able tomaintain sufficient optical signal transmission. In other words, theoptical loss is minimized. On the other hand, since the electricalsignal is transmitted to the first electrical coupling portion 510 andthe second electrical coupling portion 540, the heavily doped portions(the first electrical coupling portion 510 and the second electricalcoupling portion 540) are able to increase depletion region variationunder different voltage bias, thereby providing larger effectiverefractive index change (Δ Neff). Moreover, the ladder shaped first slabportion 520 and the ladder shaped second slab portion 550 providesufficient thickness to reduce sheet resistance, thereby minimizing theRC delay. As such, a desired bandwidth may be effectively obtained. Forexample, as compared to the straight slab portions, the ladder shapedfirst slab portion 520 and the ladder shaped second slab portion 550 areable to reduce the transmission loss by up to 14%, to reduce the slabresistance by approximately 35%, and to improve the bandwidth byapproximately 49%. Furthermore, since a PIN junction/structure is formedin the optical coupling region OR, the power consumption in the opticalmodulator 500 d may be lowered and the optical modulator 500 d may beutilized in ultra-low power applications.

FIG. 9 is a schematic cross-sectional view illustrating an opticalmodulator 500 e in accordance with some alternative embodiments of thedisclosure. Referring to FIG. 9, the optical modulator 500 e in FIG. 9is similar to the optical modulator 500 in FIG. 3D, so similar elementsare denoted by the same reference numeral and the detailed descriptionsthereof are omitted herein. The difference between the optical modulator500 e in FIG. 9 and the optical modulator 500 in FIG. 3D lies in thatthe optical modulator 500 e further includes an insulator 710 sandwichedbetween the first optical coupling portion 530 and the second opticalcoupling portion 560. In other words, at least a portion of the firstcoupling portion 530 and the second optical coupling portion 560 areseparated by the insulator 710. In some embodiments, a material of theinsulator 710 may be similar to the material of the dielectric layer 200and the insulating layer 700. For example, the material of the insulator710 may include silicon oxide, silicon nitride, titanium oxide, or thelike.

In some embodiments, since the optical signal is transmitted close to/inthe first optical coupling portion 530 and the second optical couplingportion 560, the lightly doped portions (the first optical couplingportion 530 and the second optical coupling portion 560) are able tomaintain sufficient optical signal transmission. In other words, theoptical loss is minimized. On the other hand, since the electricalsignal is transmitted to the first electrical coupling portion 510 andthe second electrical coupling portion 540, the heavily doped portions(the first electrical coupling portion 510 and the second electricalcoupling portion 540) are able to increase depletion region variationunder different voltage bias, thereby providing larger effectiverefractive index change (Δ Neff). Moreover, the ladder shaped first slabportion 520 and the ladder shaped second slab portion 550 providesufficient thickness to reduce sheet resistance, thereby minimizing theRC delay. As such, a desired bandwidth may be effectively obtained. Forexample, as compared to the straight slab portions, the ladder shapedfirst slab portion 520 and the ladder shaped second slab portion 550 areable to reduce the transmission loss by up to 14%, to reduce the slabresistance by approximately 35%, and to improve the bandwidth byapproximately 49%.

FIG. 10 is a schematic cross-sectional view illustrating an opticalmodulator 500 f in accordance with some alternative embodiments of thedisclosure. Referring to FIG. 10, the optical modulator 500 f in FIG. 10is similar to the optical modulator 500 in FIG. 3D, so similar elementsare denoted by the same reference numeral and the detailed descriptionsthereof are omitted herein. The difference between the optical modulator500 f in FIG. 10 and the optical modulator 500 in FIG. 3D lies in thatthe first optical coupling region OCR1 overlaps with the second opticalcoupling region OCR2. As illustrated in FIG. 10, the second opticalcoupling portion 560 is located underneath the first optical couplingportion 530. In some embodiments, the first optical coupling portion 530covers a top surface T₅₆₀ and a first sidewall SW_(560a) of the secondoptical coupling portion 560. On the other hand, a portion of a secondsidewall SW_(560b) is covered by the insulating layer 700 while anotherportion of the second sidewall SW_(560b) is covered by the second slabportion 550. In some embodiments, a sidewall SW₅₃₀ of the first opticalcoupling portion 530 is coplanar with the second sidewall SW_(560b) ofthe second optical coupling portion 560. In some embodiments, a widthW₅₃₀ of the first optical coupling portion 530 is greater than a widthW₅₆₀ of the second optical coupling portion 560.

In some embodiments, since the optical signal is transmitted close to/inthe first optical coupling portion 530 and the second optical couplingportion 560, the lightly doped portions (the first optical couplingportion 530 and the second optical coupling portion 560) are able tomaintain sufficient optical signal transmission. In other words, theoptical loss is minimized. On the other hand, since the electricalsignal is transmitted to the first electrical coupling portion 510 andthe second electrical coupling portion 540, the heavily doped portions(the first electrical coupling portion 510 and the second electricalcoupling portion 540) are able to increase depletion region variationunder different voltage bias, thereby providing larger effectiverefractive index change (Δ Neff). Moreover, the ladder shaped first slabportion 520 and the ladder shaped second slab portion 550 providesufficient thickness to reduce sheet resistance, thereby minimizing theRC delay. As such, a desired bandwidth may be effectively obtained. Forexample, as compared to the straight slab portions, the ladder shapedfirst slab portion 520 and the ladder shaped second slab portion 550 areable to reduce the transmission loss by up to 14%, to reduce the slabresistance by approximately 35%, and to improve the bandwidth byapproximately 49%.

In some embodiments, the ladder shaped first slab portion 520 and theladder shaped second slab portion 550 may be utilized in variousmodulators, such as a Mach-Zehnder Modulator (MZM) or a Ring Modulator(RM). In some embodiments, the MZM includes a phase shifter implementedin a doped waveguide, a Mach-Zehnder interferometer (MZI), and amulti-mode interferometer (MMI). The ladder shaped first slab portion520 and the ladder shaped second slab portion 550 may be incorporatedinto the doped waveguide of the MZM to improve the bandwidth of themodulator. In some embodiments, the RM includes a ring and a waveguideimplemented in a doped waveguide. The ladder shaped first slab portion520 and the ladder shaped second slab portion 550 may be incorporatedinto the doped waveguide of the RM to improve the bandwidth of themodulator.

In accordance with some embodiments of the disclosure, an opticalmodulator includes a dielectric layer and a waveguide. The waveguide isdisposed on the dielectric layer. The waveguide has a first region, asecond region, and an optical coupling region between the first regionand the second region. The waveguide located in the first regionincludes a first electrical coupling portion and a first slab portionconnected to each other. The waveguide located in the second regionincludes a second electrical coupling portion and a second slab portionconnected to each other. The waveguide located in the optical couplingregion includes a first optical coupling portion and a second opticalcoupling portion. The first slab portion has at least two sub-portionshaving different heights. The second slab portion has at least twosub-portions having different heights.

In accordance with some alternative embodiments of the disclosure, anoptical modulator includes a waveguide. The waveguide has a firstregion, a second region, and an optical coupling region between thefirst region and the second region. The waveguide located in the firstregion includes a first electrical coupling portion and a first slabportion connected to each other. The waveguide located in the secondregion includes a second electrical coupling portion and a second slabportion connected to each other. The waveguide located in the opticalcoupling region includes a first optical coupling portion connected tothe first slab portion and a second optical coupling portion connectedto the second slab portion. An interfacial area between the firstelectrical coupling portion and the first slab portion is larger than aninterfacial area between the first slab portion and the first opticalcoupling portion. An interfacial area between the second electricalcoupling portion and the second slab portion is larger than aninterfacial area between the second slab portion and the second opticalcoupling portion.

In accordance with some embodiments of the disclosure, a packageincludes a processor, an optical modulator, and a driver. The opticalmodulator includes a dielectric layer and a waveguide. The waveguide isdisposed on the dielectric layer. The waveguide has a first region, asecond region, and an optical coupling region between the first regionand the second region. The waveguide located in the first regionincludes a first electrical coupling portion and a first slab portionconnected to each other. The waveguide located in the second regionincludes a second electrical coupling portion and a second slab portionconnected to each other. The waveguide located in the optical couplingregion includes a first optical coupling portion and a second opticalcoupling portion. The first slab portion and the second slab portion arerespectively ladder shaped. The driver is configured to drive theoptical modulator and is electrically connected to the processor.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. An optical modulator, comprising: a dielectriclayer; a waveguide disposed on the dielectric layer, wherein thewaveguide comprises an electrical coupling portion, a slab portion, andan optical coupling portion, the slab portion is sandwiched between theelectrical coupling portion and the optical coupling portion, the slabportion has at least two sub-portions having different heights, and amaximum height of the slab portion is smaller than a height of theelectrical coupling portion.
 2. The optical modulator according to claim1, further comprising: a substrate, wherein the dielectric layer and thewaveguide are stacked on the substrate; a conductive connector disposedon the electrical coupling portion of the waveguide; and an insulatinglayer covering the waveguide and the conductive connector.
 3. Theoptical modulator according to claim 1, wherein a doping concentrationof the electrical coupling portion is greater than a dopingconcentration of the slab portion, and the doping concentration of theslab portion is greater than a doping concentration of the opticalcoupling portion.
 4. The optical modulator according to claim 1, whereinthe slab portion comprises a first sub-portion connected to theelectrical coupling portion, a second sub-portion connected to the firstsub-portion, and a third sub-portion connected to the secondsub-portion, a doping concentration of the electrical coupling portionis greater than a doping concentration of the first sub-portion, thedoping concentration of the first sub-portion is greater than a dopingconcentration of the second sub-portion, the doping concentration of thesecond sub-portion is greater than a doping concentration of the thirdsub-portion, and the doping concentration of the third sub-portion isgreater than a doping concentration of the optical coupling portion. 5.The optical modulator according to claim 1, wherein the slab portioncomprises a first sub-portion connected to the electrical couplingportion and a second sub-portion connected to the first sub-portion, anda height of the first sub-portion is greater than a height of the secondsub-portion.
 6. The optical modulator according to claim 5, wherein theslab portion further comprises a third sub-portion connected to thesecond sub-portion, and a height of the second sub-portion is greaterthan a height of the third sub-portion.
 7. The optical modulatoraccording to claim 1, wherein the height of the electrical couplingportion is equal to a height of the optical coupling portion.
 8. Theoptical modulator according to claim 1, wherein the waveguide furthercomprises an intrinsic semiconductor portion connected to the opticalcoupling portion, and the optical coupling portion is sandwiched betweenthe slab portion and the intrinsic semiconductor portion.
 9. The opticalmodulator according to claim 8, wherein a height of the intrinsicsemiconductor portion is less than a height of the optical couplingportion.
 10. The optical modulator according to claim 1, furthercomprising an insulator, wherein the optical coupling portion issandwiched between the slab portion and the insulator.
 11. An opticalmodulator, comprising: a waveguide, wherein the waveguide comprises afirst portion and a second portion next to the first portion, the firstportion comprises a first electrical coupling portion, a first slabportion connected to the first electrical coupling portion, and a firstoptical portion connected to the first slab portion, the second portioncomprises a second electrical coupling portion, a second slab portionconnected to the second electrical coupling portion, and a secondoptical coupling portion connected to the second slab portion, aninterfacial area between the first electrical coupling portion and thefirst slab portion is larger than an interfacial area between the firstslab portion and the first optical coupling portion, and a maximumheight of the first slab portion is smaller than a height of the firstelectrical coupling portion.
 12. The optical modulator according toclaim 11, wherein a doping concentration of the first electricalcoupling portion is greater than a doping concentration of the firstslab portion, and the doping concentration of the first slab portion isgreater than a doping concentration of the first optical couplingportion.
 13. The optical modulator according to claim 12, wherein adoping concentration of the second electrical coupling portion isgreater than a doping concentration of the second slab portion, and thedoping concentration of the second slab portion is greater than a dopingconcentration of the second optical coupling portion.
 14. The opticalmodulator according to claim 11, wherein the waveguide further comprisesa third portion sandwiched between the first portion and the secondportion, and the third portion comprises an intrinsic semiconductorportion sandwiched between the first optical coupling portion and thesecond optical coupling portion.
 15. The optical modulator according toclaim 11, further comprising an insulator sandwiched between the firstportion and the second portion of the waveguide.
 16. The opticalmodulator according to claim 11, wherein a width of the first opticalcoupling portion is greater than a width of the second optical couplingportion.
 17. The optical modulator according to claim 11, wherein thefirst optical coupling portion covers a top surface and a sidewall ofthe second optical coupling portion.
 18. A package, comprising: aprocessor; an optical modulator, comprising: a dielectric layer; and awaveguide disposed on the dielectric layer, wherein the waveguidecomprises an electrical coupling portion, a slab portion, and an opticalcoupling portion, the slab portion is sandwiched between the electricalcoupling portion and the optical coupling portion, and the slab portionis ladder shaped; and a driver configured to drive the opticalmodulator, wherein the driver is electrically connected to theprocessor.
 19. The package according to claim 18, wherein a dopingconcentration of the electrical coupling portion is greater than adoping concentration of the slab portion, and the doping concentrationof the slab portion is greater than a doping concentration of theoptical coupling portion.
 20. The package according to claim 18, whereina maximum height of the slab portion is smaller than a height of theelectrical coupling portion.